[collectd] PUTVAL to update multiple fields

[kgardenia42]

Hi,

I am trying to update an RRD with multiple fields using PUTVAL (from a
shell script):

I'm basically trying to do the equivalent of this:

    rrdtool update $COLLECT_PATH/agg.rrd N:100:70

Where agg.rrd has 2 fields, rx and tx (in this case with values 100
and 70 respectively).   I gather that it is usually advocated that
this sort of thing be accomplished with mupltpler RRDSs but  but I
like that the values are coupled together in this case.

Anyway, I can't seem to figure out how to accomplish the above with PUTVAL.

I have tried:
   PUTVAL $HOSTNAME/foo/agg interval=$INTERVAL N:100:70
.. but that doesn't seem to work.

I also tried:
  PUTVAL $HOSTNAME/foo/agg interval=$INTERVAL N:100 N:70

I'm sure I'm missing something trivial here.   I'd be grateful for any pointers.

Thanks.